Disease Control Newsletter (DCN)

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Influenza, 2015

Several influenza surveillance methods
are employed. Data are summarized by
influenza season (generally October-
April) rather than calendar year.

Hospitalized Cases

Surveillance for pediatric (<18 years of age)laboratory-confirmed hospitalized
cases of influenza in the metropolitan
area began during the 2003-2004
influenza season, and was expanded
statewide 2008-2009. Since the 2013-
2014 season, clinicians are encouraged
to collect a throat or nasopharyngeal
swab, or other specimen, from all
patients admitted to a hospital with
suspect influenza, and submit the
specimen to the PHL for testing. In
the 2014-2015 season, influenza B
subtyping was added.

During the 2015-2016 season, there
were 1,501 laboratory-confirmed
hospitalized cases (27.5 cases per
100,000 persons compared to 77.2
cases per 100,000 in 2014-2015)
reported. Cases included 1,327
influenza A (590 A[H1N1]pdm09, 41 H3,
and 695 unknown A type), 156 influenza
B (55 of Yamagata lineage, 3 of Victoria
lineage), 6 positive for both influenza
A and B, and 12 of unknown influenza
types. Among the cases, 16% were
0-18 years of age, 21% were 19-49
years of age, 28% were 50-64 years of
age, and 35% were ≥65 years of age.
Residents of the metropolitan area
made up 65% of cases.

Case report forms have been completed
on 70% of 976 metropolitan area cases.
Of these, 32% were diagnosed with
pneumonia, 20% required admission
into an intensive care unit, and 10%
were placed on mechanical ventilation.
An invasive bacterial co-infection was
present in 9% of hospitalized cases.
Antiviral treatment, recommended
for all hospitalized influenza cases,
was prescribed for 85% of cases.
Overall, 93% of adult cases and 45% of
pediatric cases had at least one chronic
medical condition that would have put
them at increased risk for influenza
disease.

Pediatric Deaths

There were 3 pediatric influenza-associated
deaths.

Laboratory Data

The Minnesota Laboratory System
(MLS) Laboratory Influenza Surveillance
Program is made up of more than 110
clinic- and hospital-based laboratories,
voluntarily submitting testing data on
a weekly basis. These laboratories
perform rapid testing for influenza
and respiratory syncytial virus (RSV).
Significantly fewer labs perform viral
culture testing (six labs) for influenza,
RSV, and other respiratory viruses.
Nine laboratories perform PCR testing
for influenza and three also perform
PCR testing for other respiratory
viruses. The PHL also provides further
characterization of submitted influenza
isolates to determine the hemagglutinin
serotype to indicate vaccine coverage.
Tracking laboratory results assists
healthcare providers with patient
diagnosis of influenza-like illness
(ILI) and provides an indicator of the
progression of the influenza season
as well as prevalence of disease in the
community. Between October 4, 2015
- May 21, 2016, laboratories reported
data on 21,273 influenza PCR tests,
1,617 (8%) of which were positive for
influenza. Of these, 687 (43%) were
positive for influenza A(H1N1)pdm09,
21 (1%) were positive for influenza
A/(H3), 649 (40%) were positive for
influenza A-not subtyped, and 260
(16%) were positive for influenza B.

Sentinel Surveillance

We conduct sentinel surveillance for ILI
(fever >100° F and cough and/or sore
throat in the absence of known cause
other than influenza) through outpatient
medical providers including those in
private practice, public health clinics,
urgent care centers, emergency rooms,
and university student health centers.
There are 26 sites in 22 counties.
Participating providers report the total
number of patient visits each week and
number of patient visits for ILI by age
group (0-4 years, 5-24 years, 25-64
years, ≥65 years). Percentage of ILI
peaked during the week of March 6-12,
2016 at 2.4%.

Influenza Incidence Surveillance Project

MDH was one of eight nationwide sites
to participate in an Influenza Incidence
Surveillance Project for the 2015-2016
influenza season. Four clinic sites
reported the number of ILI patients and
acute respiratory illness (ARI; recent
onset of at least two of the following:
rhinorrhea, sore throat, cough, or fever)
patients seen within five age groups,
each week. Clinical specimens were
collected on the first 10 patients with
ILI and the first 10 patients with ARI for
PCR testing at the PHL for influenza
and 13 other respiratory pathogens.
Minimal demographic information and
clinical data were provided with each
specimen.

ILI Outbreaks (Schools and Long Term Care Facilities)

Between 1988 and 2009, a probable
ILI outbreak in a school was defined
as a doubled absence rate with
primary influenza symptoms reported
among students. The definition of ILI
outbreaks changed with the 2009-2010
school year. Schools reported when
the number of students absent with
ILI reached 5% of total enrollment, or
when three or more students with ILI
are absent from the same elementary
classroom. Ninety-two schools in 35
counties reported ILI outbreaks during
the 2013-2014 school year. This is the
lowest number of schools reporting ILI
outbreaks since the 2009-2010 school
year when the highest was 1,302
schools in 85 counties in 2009-2010.

An influenza outbreak is suspected in a
long-term care facility (LTCF) when two
or more residents in a facility develop
symptoms consistent with influenza
during a 48- to 72-hour period. An
influenza outbreak is confirmed when
at least one resident has a positive culture, PCR, or rapid antigen test for
influenza and there are other cases
of respiratory illness in the same unit.
Forty-eight facilities in 23 counties
reported confirmed outbreaks during
the 2015-2016 influenza season. The
number of LTCFs reporting outbreaks
ranged from a low of three in 2008-2009
to a high of 209 in 2012-2013.